The technical field of the present invention covers connection systems for high-voltage currents (several tens of kv).
In this field the industrial applications sometimes require cables carrying high-voltage currentsxe2x80x94which also may exhibit of high and variable densitiesxe2x80x94to cross what in general are metallic walls. A particular problem arises when a vacuumxe2x80x94or sealing relative to another gasxe2x80x94must be maintained on one side of the wall. The same difficulty is encountered when two cables of this kind must be connected in vacuum.
Several types of connection systems are presently available to solve the problem of high-voltage cable connection or wall feedthroughs. Such devices can be found in high-voltage coax(ial) connector catalogues published by specialized suppliers such as RADIALL, ALCATEL, ETAT, LEYBOLD, PFEIFFER, VARIAN or VEECO. Most of these devices consist of a set of a male and female connector elements (to connect one insulated coaxial line to another which is also insulated) or of a wall-mounted connector element and a plug (when joining an insulated coax line to a non-insulated line in air). One of the two connector elements, or the wall-mounted connector element, is then affixed to the wall being crossed and hermeticity is assured by conventional seals on the two sides of the wall.
However, because these connector elements entail electrical contact and a break in dielectric on each side of the wall, they will operate properly under high voltage only if the connection is implemented at atmospheric pressure. As soon as these connector elements are made to operate in vacuum, arcing arises at the surface along the dielectric junctions of the connection systems and the voltage drops.
Moreover the conventional plug-jack connections entail high inductance on account of the substantially different diameters of the inner and outer conductors, said high inductances hampering rapid pulse propagation for instance from a capacitor discharge through the connection. While operation remains feasible by increasing the power of the current generator when using DC, the problem becomes practically prohibitively difficult if a high current is desired by a very fast capacitor discharge.
Moreover the conventional connection systems permanently affix either the case of one of the connectors, or the wall-mounted element to the wall, thereby precluding rapid engagement and disengagement of the cable ends with and from the wall.
Therefore it is the objective of the present invention to create a connection system wherein the dielectrics remain immersed in a gas atmosphere or any other fluid even when part of the connection system is in a vacuum. The invention moreover implements its connection by retaining a coaxial geometry which is close to that of the cables and in this manner allows easily disengaging both cables from the wall to which they are mounted.
The connection systems of the invention are able to withstand voltages that per se do not restrict the application of this invention, even in a deep vacuum, because the configuration of the invention, by means of an increase in length of the connection system, allows adjusting its arcing strength merely by increasing the length of the dielectric on which the electric arc might travel. Significantly the increase in length does not entail increased radial bulk, and consequently the connection inductance is not increased.
For that purpose the invention proposes a connection system comprising a metal outer shell connected to the grounding braids of the cables to be joined, furthermore a dielectrically insulating sleeve inside said metal shell and enclosing the inner conductors of the two cables and their insulating sheaths, said connection system being fitted with a sealed cavity between the insulating sheaths of the cables being joined and the insulating, dielectric sleeve; said cavity is always exposed to a gas, preferably atmospheric air introduced in the cavity during assembly, or it remains filled with a hydraulic fluid even when the connection system or part of it is placed into an enclosure under vacuum. The gas pressure or the presence of the fluid shall be preserved in said cavity by using seals situated on one hand on the end of one of the two cables and on the other hand between the dielectrics of the particular cable sheath and the end of the insulating sleeve. Sealing the cable end must be implemented both on the inner cable conductor to preclude leaks through the cable inside and on the insulating sheath in order to attain the desired sealed cavity.
Where the cable must cross a wall separating a gas atmosphere from an enclosure at vacuum, sealing can be implemented only at one end of the dielectric sleeve; on the other hand, if the connection system is meant to be fully situated in a vacuum, sealing will be required at the ends of both cables and at the ends of the insulating sleeve.
Preferably the outer metal shell and the dielectric, insulating sleeve exhibit a cylindrical cross-section in order to enclose at minimal bulk the cable ends and hence entailing minimal inductance, further to assure good shielding against electromagnetic radiations. Moreover said shell and sleeve also may consist of two tubes, one being metallic, the other a dielectric, which nest in each and are affixed to each other. In particular this configuration offers the advantage of easily positioning the cables inside the metal shell and dielectric insulating sleeve and facilitate maintenance of the assembly.
Preferably the cable end may be sealed by a plug crimped on the cable and its insulating sheath. If necessary the plug shall be soldered on the inner conductor to seal off the inside of the cable inner conductor.
Preferably the cavity at the end of the sleeve is sealed by inserting an O-ring between the insulating sleeve""s dielectric and the dielectric of the insulating sheath of the cable being hooked up.
To assure easy dismantling of the two cables from the wall, the invention proposes that the cable ends, which preferably are fitted with plugs soldered onto the inner conductors, shall be connected using jacks receiving said plugs.
Lastly dismantling is made easy by adding detachable fasteners of the cables"" metal sheaths on the outer metal sheath.
This device of the invention offers the advantage allowing connecting high-voltage carrying coax cablesxe2x80x94where said voltages may reach and even exceed 100 kvxe2x80x94and to make use of such cables at very low pressures, and even in a deep vacuum that may be as low as 10xe2x88x927 mbars, this limit being set by the mechanical strength of the elastomer dielectrics in vacuum and the associated surface degassing, without electric discharges taking place at the junctions between the dielectrics.
Said device of the invention also allows making the connection without generating electromagnetic interference thanks to the shielding continuity around these elements.
Another advantage of the invention is that the proposed axial geometry of the opposite dielectric, namely the insulating sleeve dielectric and the insulating sheath dielectric of the cable, entails a connection inductance which is close to that of the cable and that consequently this kind of connection system assures the transmission of high-voltage electric pulses at minimal losses caused by counter-electromotive forces. By preserving the axial structure, the advantages of the low-voltage connection systems are thus retained.
Moreover the axial configuration offers the advantage that this connection takes place in a cylindrical volume of small diameter.
Lastly the device of the invention offers the advantage that with regard to its application as a wall feedthrough, it is easy to affix the cables to and remove them from the wall.